Recently, it has become desirable to obtain silver halide photographic materials which can be processed by rapid processing and which have high sensitivity and can form good images with high image quality with respect to tone reproducibility.
For instance, in photographic laboratories for color development, the necessity of rapid processing is increasing since shortening of processing time improves photographic production efficiency and reduces production cost. Additionally, elevation of the sensitivity of not only picture-taking photographic materials but also printing photographic materials is also desired, since shortening the exposure time for printing produces the same effects noted above.
Various approaches have heretofore been suggested for a rapid processing system for both picture-taking and printing photographic materials themselves, as well as the processing solutions to be used for processing the materials. For instance, with respect to color development procedure, various means of elevation of the temperature of processing solutions, elevation of the pH value thereof and addition of color developing agents of high concentration have been attempted. Additionally, a means of adding various additives such as a development promoter has also been known.
As examples of usable development promoters, there are known 1-phenyl-3-pyrazolidone described in British Patent 811,185, N-methyl-p-aminophenol described in U.S. Pat. No. 2,417,514, and N,N,N',N'-tetramethylphenylenediamine described in JP-A-50-15554. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, the known means could not attain sufficiently rapid processing and are often accompanied by undesirable deterioration of characteristics of processed materials such as elevation of fog.
On the other hand, it is known that the shape, size and composition of silver halide grains in the silver halide emulsions to be in photographic materials have a great influence on the rate of development. In particular, the halogen composition has an especially great influence thereon. In this connection, it is known that a silver halide emulsion having a high silver chloride content displays an extremely high rate of development.
However, such a high-silver chloride emulsion is not always advantageous for elevating of the sensitivity of photographic materials. As for such high silver chloride emulsions, JP-A-58-108533 corresponding to U.S. Pat. No. 4,564,591 and JP-A-60-222845 corresponding to U.S. Pat. No. 4,605,610, European Patents 0,273,430 and 0,273,429 and JP-A-1-177531 mention that providing a silver halide-localized phase in high-silver chloride grains is effective for elevating the sensitivity of photographic materials containing the grains.
Regarding a silver halide emulsion comprising grains having different halogen composition-localized phases, there are known, for example, a silver chloride-conjugated silver iodide emulsion described in JP-A-53-103725 corresponding to U.S. Pat. No. 4,094,684 and a silver chlorobromide emulsion comprising cubic grains with different halogen composition in the corners thereof described in JP-A-55-124139 corresponding to U.S. Pat. No. 4,496,652.
JP-A-62-89949 corresponding to U.S. Pat. No. 4,735,894 describes grains having different halogen compositions as grown on the (100) plane of the silver halide crystal.
In order to meet the demand for rapid processing in the photographic market, it is advantageous to employ high-silver chloride emulsion-containing photographic materials.
However, high-silver chloride emulsions are not always advantageous for elevation of the sensitivity of photographic materials, as mentioned above. Though the sensitivity of such high-silver chloride emulsion-containing photographic materials could be improved to some degree by the methods described in the above-mentioned patent publications, the improvement is limited.
For instance, in any of the techniques described in JP-A-58-108533 and JP-A-60-222845 and European Patent 0,273,430, the photographic materials containing the proposed silver halide emulsions have a disadvantage in that the gradation of the image to be formed thereon is softer, especially in the shoulder part, than the originally intended image.
JP-A-53-103725 mentions emulsions which are not applicable to rapid processing since the emulsions have a high silver iodide content. Emulsions proposed in JP-A-55-124139 give a soft gradation, and emulsions proposed in JP-A-62-89949 do not have a sufficient reciprocity law characteristic.
Thus, all the known high-silver chloride emulsions are not satisfactorily practical but need to be improved with respect to both sensitivity and gradation. Additionally, with respect to the reciprocity law characteristic, the emulsions also have various problems with the soft contrast in high intensity exposure, the soft contrast in low intensity exposure and the low sensitivity.
Accordingly, there is an extremely strong demand for high-silver chloride emulsions and high-silver chloride photographic materials having a higher sensitivity, a harder gradation and a better reciprocity law characteristic.